Functional alloy plating using substitute bonding material for Pb and electronic component to be mounted to which the functional alloy plating is applied

ABSTRACT

The present invention relates to a to-be-mounted electronic component to which functional alloy plating using a bonding material for mounting is applied with a substitute bonding material for solder (tin-lead alloy), and aims at providing alloy plating which has been put to a practical use in such a way that the function of existing alloy plating of this type has been significantly improved to eliminate toxic plating from various kinds of electronic components for use in electronic devices so that it is useful in protecting the environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 09/566,125 filed May 5, 2000 now U.S. pat. No. 6,478,944, andwhich claims priority of Japanese Application No. 11-164307, filed May7, 1999. The entire disclosure of application Ser. No. 09/566,125 isconsidered as being part of the disclosure of this application, and theentire disclosure of application Ser. No. 09/566,125 is expresslyincorporated by reference herein in its entirety.

DETAILED DESCRIPTION OF THE INVENTION

[Field of Utilization in Industry]

The present invention relates to a to-be-mounted electronic component towhich functional alloy plating using a bonding material for mounting isapplied with a substitute bonding material for solder (tin-lead alloy),and aims at providing alloy plating which has been put to a practicaluse in such a way that the function of existing alloy plating of thistype has been significantly improved to eliminate toxic plating fromvarious kinds of electronic components for use in electronic devices sothat it is useful in protecting the environment.

[Background of the Invention]

As solder which does not use lead (Pb) (Pb-free solder), various newbonding agents have been developed and their properties become apparent.And, the stage is proceeding to the development of their manufacturingmethods. Tin (Sn)-bismuth (Bi), Sn-indium alloy (In), Sn-zinc alloy(Zn), Sn plating etc. are considered as Pb-free solder to devices. Thecost for the Sn—In alloy among them is extremely high, about 25 timesthe cost for Sn—Bi. The Sn—Zn alloy has a problem on the solderabilityafter heat resistance because Zn is prone to be oxidized. This leavesSn—Ag, Sn—Bi and Sn.

Bi on copper may be thermally diffused at the time of reflow and may bepeeled, so that Sn—Bi for devices should have nickel applied as a basein order to avoid the peeling.

If a coat offset (melt-originated offset) occurs when a surface-mountingdevice is melted, the bonding surface has a rough surface, so that thebonding surface becomes smaller, thus lowering the bonding strength.Prevention of a melt-originated offset which makes organic eutectoid ina coat extremely small is attempted by applying plating according tothis invention.

[Prior Art]

Conventionally, solder (tin-lead alloy) has been used for a long time asa bonding material for mounting electronic device components. Recently,the harmfulness of lead has been noticed mainly in America and Europeand removal of lead from electronic devices has progressed rapidly.

Meanwhile, in Japan has already started a movement of voluntary removalmainly by the electronics industry.

Electroplating is applied to most of materials for to-be-mountedelectronic components as tinning. Therefore, there is a pressing need toindustrialize plating of substitute alloys for the industrial growth.

[Problem to be Solved by the Invention]

As solder which is an essential bonding material for the aforementionedelectronic components contain lead (Pb), however, when electronicdevices are disposed of, lead would be melted and seep into groundwaterfrom a junk yard, raising a problem of environmental pollution, unlesselectronic components having to-be-mounted parts containing solder'slead are removed.

[Means for Solving the Problem]

Accordingly, it is an object of this invention to overcome the problemof the prior art and to provide electronic components to be on whichvery practical alloy plating for bonding that is the existing alloyplating of this type which has been improved significantly is appliedusing a substitute metal for lead in solder alloy plating.

The first of this invention is functional alloy plating using substitutebonding material for Pb and electronic component to be mounted to whichthe functional alloy plating is applied, characterized in that with Snas a base, one of Bi, Ag and Cu is selected, a Bi content to the Sn isset to 1.0% or less, the Bi content to the Sn is set to 2.0 to 10.0%, anAg content to the Sn is set to 1.0 to 3.0%, the Ag content to the Sn isset to 3.0 to 5.0%, the Ag content to the Sn is set to 8.0 to 10.0%, ora Cu content to the Sn is set to 0.5 to 1.0%, and an electrolyticprocess is performed with a special waveform.

The second of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an IC chip is wire-bonded to a lead frame and outer leadsexposed outside a molded IC package are subjected to an electrolyticprocess with a Bi content to Sn whose content is 99.0% or greater beingset to 1.0% or less and with a special waveform.

The third of this invention is functional alloy plating using substitutebonding material for Pb and electronic component to be mounted to whichthe functional alloy plating is applied, characterized in that an ICchip is wire-bonded to a lead frame and outer leads exposed outside amolded IC package are subjected to an electrolytic process with a Bicontent to Sn whose content is 98.0 to 90.0% being set to 2.0 to 10.0%and with a special waveform.

The fourth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an IC chip is wire-bonded to a lead frame and outer leadsexposed outside a molded IC package are subjected to an electrolyticprocess with an Ag content to Sn whose content is 99.0 to 97.0% beingset to 1.0 to 3.0% and with a special waveform.

The fifth of this invention is functional alloy plating using substitutebonding material for Pb and electronic component to be mounted to whichthe functional alloy plating is applied, characterized in that an ICchip is wire-bonded to a lead frame and outer leads exposed outside amolded IC package are subjected to an electrolytic process with an Agcontent to Sn whose content is 97.0 to 95.0% being set to 3.0 to 5.0%and with a special waveform.

The sixth of this invention is functional alloy plating using substitutebonding material for Pb and electronic component to be mounted to whichthe functional alloy plating is applied, characterized in that an ICchip is wire-bonded to a lead frame and outer leads exposed outside amolded IC package are subjected to an electrolytic process with an Agcontent to Sn whose content is 92.0 to 90.0% being set to 8.0 to 10.0%and with a special waveform.

The seventh of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an IC chip is wire-bonded to a lead frame and outer leadsexposed outside a molded IC package are subjected to an electrolyticprocess with a Cu content to Sn whose content is 99.5 to 99.0% being setto 0.5 to 1.0% and with a special waveform.

The eighth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an electrode pattern of a printed circuit board is subjected toan electrolytic process with a Bi content to Sn whose content is 99.0%or greater being set to 1.0% or less and with a special waveform.

The ninth of this invention is functional alloy plating using substitutebonding material for Pb and electronic component to be mounted to whichthe functional alloy plating is applied, characterized in that anelectrode pattern of a printed circuit board is subjected to anelectrolytic process with a Bi content to Sn whose content is 98.0 to90.0% being set to 2.0 to 10.0% and with a special waveform.

The tenth of this invention is functional alloy plating using substitutebonding material for Pb and electronic component to be mounted to whichthe functional alloy plating is applied, characterized in that anelectrode pattern of a printed circuit board is subjected to anelectrolytic process with an Ag content to Sn whose content is 99.0 to97.0% being set to 1.0 to 3.0% and with a special waveform.

The eleventh of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an electrode pattern of a printed circuit board is subjected toan electrolytic process with an Ag content to a content of 97.0 to 95.0%being set to 3.0 to 5.0% and with a special waveform.

The twelfth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an electrode pattern of a printed circuit board is subjected toan electrolytic process with an Ag content to a content of 92.0 to 90.0%being set to 8.0 to 10.0% and with a special waveform.

The thirteenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that an electrode pattern of a printed circuit board is subjected toan electrolytic process with a Cu content to Sn whose content is 99.5 to99.0% being set to 0.5 to 1.0% and with a special waveform.

The fourteenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that a chip tantalum capacitor is wire-bonded to a lead frame andouter leads exposed outside the chip tantalum capacitor are subjected toan electrolytic process with a Bi content to Sn whose content is 99.0%or greater being set to 1.0% or less and with a special waveform.

The fifteenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that a chip tantalum capacitor is wire-bonded to a lead frame andouter leads exposed outside the chip tantalum capacitor are subjected toan electrolytic process with a Bi content to Sn whose content is 98.0 to90.0% being set to 2.0 to 10.0% and with a special waveform.

The sixteenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that a chip tantalum capacitor is wire-bonded to a lead frame andouter leads exposed outside the chip tantalum capacitor are subjected toan electrolytic process with an Ag content to Sn whose content is 99.0to 97.0% being set to 1.0 to 3.0% and with a special waveform.

The seventeenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that a chip tantalum capacitor is wire-bonded to a lead frame andouter leads exposed outside the chip tantalum capacitor are subjected toan electrolytic process with an Ag content to Sn whose content is 97.0to 95.0% being set to 3.0 to 5.0% and with a special waveform.

The eighteenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that a chip tantalum capacitor is wire-bonded to a lead frame andouter leads exposed outside the chip tantalum capacitor are subjected toan electrolytic process with an Ag content to Sn whose content is 92.0to 90.0% being set to 8.0 to 10.0% and with a special waveform.

The nineteenth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that a chip tantalum capacitor is wire-bonded to a lead frame andouter leads exposed outside the chip tantalum capacitor are subjected toan electrolytic process with a Cu content to Sn whose content is 99.5 to99.0% being set to 0.5 to 1.0% and with a special waveform.

The twentieth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that general electronic device component materials including acomponent material which needs plating for bonding and a generalcomponent material which needs plating as a functional component aresubjected to an electrolytic process with a Bi content to Sn whosecontent is 99.0% or greater being set to 1.0% or less and with a specialwaveform.

The twenty-first of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that general electronic device component materials including acomponent material which needs plating for bonding and a generalcomponent material which needs plating as a functional component aresubjected to an electrolytic process with a Bi content to Sn whosecontent is 98.0 to 90.0% being set to 2.0 to 10.0% and with a specialwaveform.

The twenty-second of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that general electronic device component materials including acomponent material which needs plating for bonding and a generalcomponent material which needs plating as a functional component aresubjected to an electrolytic process with an Ag content to Sn whosecontent is 99.0 to 97.0% being set to 1.0 to 3.0% and with a specialwaveform.

The twenty-third of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that general electronic device component materials including acomponent material which needs plating for bonding and a generalcomponent material which needs plating as a functional component aresubjected to an electrolytic process with an Ag content to Sn whosecontent is 97.0 to 95.0% being set to 3.0 to 5.0% and with a specialwaveform.

The twenty-fourth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that general electronic device component materials including acomponent material which needs plating for bonding and a generalcomponent material which needs plating as a functional component aresubjected to an electrolytic process with an Ag content to Sn whosecontent is 92.0 to 90.0% being set to 8.0 to 10.0% and with a specialwaveform.

The twenty-fifth of this invention is functional alloy plating usingsubstitute bonding material for Pb and electronic component to bemounted to which the functional alloy plating is applied, characterizedin that general electronic device component materials including acomponent material which needs plating for bonding and a generalcomponent material which needs plating as a functional component aresubjected to an electrolytic process with a Cu content to Sn whosecontent is 99.5 to 99.0% being set to 0.5 to 1.0% and with a specialwaveform.

[Embodiment]

[Significance of Special Waveform]

A description will now be given of the aforementioned “electrolyticprocess with a special waveform”. First, typical electroplating is DCplating, i.e., plating with a voltage having an AC voltage rectified bya rectifier.

To perform plating, it is necessary to combine and add several types oforganic additives into a plating solution so that the crystal grain sizeof metal to be deposited does not become resin particle size.

Of course, those organic materials become eutectoid at the same time asthe metal to be plated, causing many defects on their functions asbonding materials.

The “electrolytic process with a special waveform” in this inventionimproves those shortcomings, and an additive to be added into a platingsolution is only a slight amount of a surface active agent which is notdecomposed and disposed, and this special waveform serves as an organicadditive.

In this invention, the special waveform is a pulse waveform which isacquired for an electrolytic process from a current that has beenrectified with a thyristor 6-phase half wave. Thus, the electrolyticprocess uses a pulse waveform which can cycle between positive andnegative.

The following shows a table of the types of mass-producible platings.

TABLE 1 Melt-originated Coats Composition offset Note Sn—Ag Ag 10%special ◯ Plating by special waveform plating waveform method of thisinvention Sn—Ag Ag 3% special X Melt-originated offset waveform platingpresent even with plating by special waveform method of this inventionSn—Bi Bi 3% special ◯ Plating by special waveform plating waveformmethod of this invention Sn Sn 100% X Normal gloss plating Sn Sn 99%special ◯ Plating by special waveform plating waveform method of thisinvention Sn—Pb Pb 10% special ◯ Plating to which waveform platingexisting chip tantlum is applied

As there are different coat characteristics to be acquired depending onwhether the lead types of devices to be used are lead lines, a leadframe or leadless, they should be selectively used, but the added valuesof the devices differ device by device so that a cost-based selection isalso considered as an important factor.

In the comparison of the costs for plating materials, the cost for thebase acid is high even if an inexpensive metal is used, so that the costdoes not decrease as indicated in the comparison of the prices ofmetals. A further variation is seen when it is run as plating.

Then, the following table shows the evaluation of Pb-free coats ascoats.

TABLE 2 Types of coats Contents Note Sn—Ag plating Ag 3-10% Meltingpoint of 220-260° C. Melt-originated offset occurred by C, Agcomposition. Glossy appearance Sn—bi plating special waveform Meltingpoint of 220-225° C. plating containing Fragile due to diffusion of Biof 2-5% Bi into C, copper base. Glossless appearance Sn platingDifferent type Melting point of 225-230° C. of metal of 0.2-1% Goodreflow. Semi-gloss contained as appearance additive

The following table shows a list of the evaluation of the individualcoats.

TABLE 3 Sn—Ag Sn—Bi Sn Appearance Gloss Glossless Semi-gloss Plating4.03 μm 4.21 μm 3.99 μm thickness Composition Sn 92.46% Sn 97.31% Sn99.84% Ag 7.54% Bi 2.69% Bi 0.16% Heat Discoloration Passed Passedresistance present Solderability Passed Passed Passed after heatresistance Bending after Passed Passed Passed heat resistance Peelingafter Passed Passed Passed heat resistance Melt-originated Present NoneNone offset Solder Zero-cross Zero-cross Zero-cross wettability 0.65 sec0.85 sec 0.50 sec before heat Wet strength Wet strength Wet strengthresistance 71.4 mg 23.0 mg 31.4 mg Solder Zero-cross Zero-crossZero-cross wettability 0.95 sec 0.87 sec 0.61 sec after heat Wetstrength Wet strength Wet strength resistance 26.4 mg 23.0 mg 34.2 mgBonding 0.37 Kg before 1.56 Kg before 1.63 Kg before strength heat heatheat resistance resistance resistance 0.05 Kg after 0.05 Kg after 0.70Kg after heat heat heat resistance resistance resistance Vickers 16.323.0 11.4 hardness

The following table shows the costs for the individual coats.

TABLE 4 Price of Sample price prototype Price in massproduction (¥/Kg)(¥/Kg) (¥/Kg) Sn—Ag 2,352 2,114 1,685 Sn—Bi 1,488 1,363 1,148 Sn specialwave- 1,518 1,518 1,089 form plating Special waveform — — — plating

While the samples shown above had a nickel (Ni) base to avoid diffusionon copper, Sn—Ag showed such a phenomenon that oxidization on Ni throughAg at the time of heat resistance lowered the bondability. In thisrespect, it is contemplated that copper (Cu) is suitable as the base forSn—Ag. Further, heat-resistance-originated discoloration andmelt-originated offset also occurred. To cope with this melt-originatedoffset, it is necessary to obtain Sn—Ag plating containing 85% or moreof Ag, which is naturally a factor to increase the cost. Slightsegregation is seen on the surface of Sn—Bi. Sn—Ag and Sn-specialwaveform plating still suffer poor solution efficiencies and the linespeeds remain about a half the speed of the current special-waveformplating. Although solution conditions were so set as to provide theoptimal appearance in the implementation of the scheme, improvements canbe made on the density of the solution, the density of the additive,stirring and so forth. In the case of surface mounting, there may be aquestion on the behavior of Bi, such as segregation or diffusion. Inthis respect, Bi in the Sn-special waveform plating has a minute amountand serves to adjust the deposition of the plated coat so that it doesnot seem to raise a problem on segregation or diffusion.

The following gives the results of the evaluation of samples of Sn—Ag,Sn—Bi and Sn plating to chip tantalum frames.

(1) Plating Specifications

-   -   base plating . . . Ni 0.5 to 1.0 μm        -   (same for all)    -   finishing plating . . . Sn—Ag 3.0 to 5.0 μm        -   Sn—Bi 3.0 to 5.0 μm        -   Sn 3.0 to 5.0 μm            (2) Test Results    -   “Sn—Ag”    -   a. Appearance: passed (free of spot, stain and discoloration)    -   b. Heat resistance: discoloration present (160° C.×6 Hr heat        resistance, no expansion, peeling, discoloration and fall-off)    -   c. Solderability test: passed (after heat resistance, 230° C.×3        sec×once n=1)    -   d. Bending test: passed (after heat resistance, 180° C.,        bend-back test, measured at A n=1)    -   e. Melt-originated: no melt-originated offset (no heat offset        resistance 270° C.×30 min×once n=1)    -   f. Peeling test: passed (sample before and after heat resistance        n=1)    -   g. Melting point: 222° C.    -   h. Hardness (Vickers hardness): 16.3    -   i. Solder: zero-cross time before heat resistance wettability        average 0.65 (sec) after heat resistance average 0.95 (sec)        -   : wet strength before heat resistance average 71.40 (mg)            after heat resistance average 26.40 (mg) (n=5)    -   j. Bonding: before heat resistance average 0.37 (kg) strength:        after heat resistance average 0.05 (kg) (n=5)    -   k. Plating thickness: average 4.03 (μm) (measured with        fluorescent X rays n=9)    -   l. Composition: Sn 92.46%        -   : Ag 7.54%    -   “Sn—Bi”    -   a. Appearance: passed (free of spot, stain and discoloration)    -   b. Heat resistance: passed (160° C.×6 Hr heat resistance, no        expansion, peeling, discoloration and fall-off)    -   c. Solderability test: passed (after heat resistance, 230° C.×3        sec×once n=1)    -   d. Bending test: passed (after heat resistance, 180° C.,        bend-back test, measured at A n=1)    -   e. Melt-originated: no melt-originated offset (no heat offset        resistance 270° C.×30 min×once n=1)    -   f. Peeling test: passed (sample before and after heat resistance        n=1)    -   g. Melting point: 228° C.    -   h. Hardness (Vickers hardness): 23.0    -   i. Solder: zero-cross time before heat resistance wettability        average 0.85 (sec) after heat resistance average 0.87 (sec)        -   : wet strength before heat resistance average 23.0 (mg)            after heat resistance average 23.0 (mg) (n=5)    -   j. Bonding: before heat resistance average 1.56 (kg) strength:        after heat resistance average 0.56 (kg) (n=5)    -   k. Plating thickness: average 4.21 (μm) (measured with        fluorescent X rays n=9)    -   l. Composition: Sn 97.31%        -   : Bi 2.69% (measured at A)    -   “Sn”    -   a. Appearance: passed (free of spot, stain and discoloration)    -   b. Heat resistance: discoloration present (160° C.×6 Hr heat        resistance. no expansion, peeling, discoloration and fall-off)    -   c. Solderability test: passed (after heat resistance, 230° C.×3        sec×once n=1)    -   d. Bending test: (after heat resistance, 180° C., bend-back        test, measured at A n=1)    -   e. Melt-originated: no melt-originated offset (no heat offset        resistance 270° C.×30 min×once n=1)    -   f. Peeling test: passed (sample before and after heat resistance        n=1)    -   g. Melting point: 232° C.    -   h. Hardness (Vickers hardness): 11.40° C.    -   i. Solder: zero-cross time before heat resistance wettability        average 0.50 (sec) after heat resistance average 0.61 (sec)        -   : wet strength before heat resistance average 31.40 (mg)            after heat resistance average 34.20 (mg) (n=5)    -   j. Bonding: before heat resistance average 1.63 (kg) strength:        after heat resistance average 0.70 (kg) (n=5)    -   k. Plating thickness: average 3.99 (μm) (measured with        fluorescent X rays n=9)    -   l. Composition: Sn 99.84%        -   : Bi 0.16% (measured at A)            (3) Evaluation Method and Data

-   {circle around (1)} Hardness (Vickers Hardness) Measuring Conditions    Measure portion “A” of non-heat-resisted samples under the following    conditions by using a super light load minute hardness meter (model    mvk-1).    -   a. load: 0.5 fg    -   b. load keeping time: 15 sec    -   c. load speed: 0.01 mm/sec Measure the diagonal line of a dent        three times and compute the Vickers hardness from the average        dent area.

-   {circle around (2)} Zero-Crossing Time, Wet Strength Measuring    Conditions    -   Five portions “A” of samples S of a frame were sampled from one        piece shown in FIG. 1 and were measured under the following        conditions using a solder checker (SAT-2000).    -   a. Sn 60%, Pb 40%    -   b. TEMP 230° C., SPEED 25 mm/sec    -   c. DEPTH 2 m, SENS 1    -   d. Flux present (MI L type R used)        (4) Solder Wettability Data

-   {circle around (1)} The solder wettability data of Sn—Ag is    illustrated in Table 5.

TABLE 5 Sn—Ag Data Average Zero-cross before 0.65 0.69 0.63 0.67 0.600.65 heat resistance (sec) after heat 1.02 0.90 0.80 1.00 1.05 0.95resistance Wet strength before 84.0 69.0 81.0 55.0 68.0 71.4 heatresistance (mg) after heat 32.0 23.0 27.0 20.0 30.0 26.4 resistance

-   {circle around (2)} The solder wettability data of Sn—Bi is    illustrated in Table 6.

TABLE 6 Sn—Bi Data Average Zero-cross before 1.01 0.82 0.97 0.62 0.830.85 heat resistance (sec) after heat 0.76 0.85 0.99 0.89 0.88 0.87resistance Wet strength before 16.0 24.0 19.0 35.0 21.0 23.0 heatresistance (mg) after heat 25.0 22.0 24.0 20.0 24.0 23.0 resistance

-   {circle around (3)} The solder wettability data of Sn is illustrated    in Table 7.

TABLE 7 Sn Data Average Zero-cross before 0.49 0.49 0.34 0.54 0.64 0.50heat resistance (sec) after heat 0.73 0.49 0.61 0.59 0.63 0.61resistance Wet strength before 27.0 34.0 44.0 28.0 24.0 31.4 heatresistance (mg) after heat 28.0 41.0 32.0 37.0 33.0 34.2 resistance(5) Bonding Strength Measuring Conditions

-   -   Cut portion “C” under leads at 3 mm in width, and sample ten        from two pieces. Place cut samples one on another with a        clearance of 0.3 mm and solder-dip under the following        conditions using a solder checker.    -   a. Sn 60%, Pb 40%    -   b. TEMP 230° C., SPEED 25 mm/sec    -   c. DEPTH 2 mm, SENS 1    -   d. Flux present (MI L type R used)    -   Measure the force to peeling by using a push-pull gauge.

TABLE 8 Sn—Ag Data Average Sample before heat 0.38 0.29 0.53 0.37 0.280.37 resistance Sample after heat 0.03 0.07 0.08 0.02 0.05 0.05resistance

TABLE 9 Sn—Bi Data Average Sample before heat 1.30 1.54 1.23 1.52 2.211.56 resistance Sample after heat 0.53 0.35 0.74 0.54 0.65 0.56resistance

TABLE 10 Sn—Bi Data Average Sample before heat 1.32 1.82 1.62 1.57 1.831.63 resistance Sample after heat 0.57 0.62 0.60 1.01 0.69 0.70resistance(6) Plating Thickness Measuring Portion

-   -   Three portions “A”, “a” and “b” of a sample S of a frame per        piece were measured and as there were five pieces of frames, a        total of nine portions, both ends and the center, were measured        using fluorescent X rays.

TABLE 11 Left end Average Sn—Ag of frame Center Right end (μm) Measuring3.99 4.04 4.10 portion A a 3.85 3.97 4.05 b 4.07 4.21 4.03 4.03

TABLE 12 Left end Average Sn—Bi of frame Center Right end (μm) Measuring4.29 3.95 3.75 portion A a 4.08 4.31 4.27 b 4.47 4.54 4.21 4.21

TABLE 13 Left end Average Sn—Ag of frame Center Right end (μm) Measuring4.53 3.79 3.70 portion A B 4.27 3.83 3.95 C 3.99 3.94 3.89 3.99(7) Measuring Portions

As shown in FIG. 1, the measuring portions “A” and “B” of the sample Sof the frame may indicate other portions of the same shapes in onepiece. That is, it means that they include the measuring portion “A” andportions “a” and “b” or the like.

With regard to the evaluation coats, evaluation method and measuringmethod, the results of the comparison of the characteristics of theindividual Pb-free coats as shown in Tables 14 to 16 were obtained.

TABLE 14 Evaluation Composition coats Names (Remainder: Sn) Note Sn—AgAg 3.0-5.0% Sn—Bi Bi 1.0-3.0% Sn-special Bi 0.1-0.5% Sn coat for surfacewaveform plating mount As-special Pb 5.0-15.0% Solder coat (As waveformplating bathed) for surface mount BF-special Pb 5.0-15.0% Solder coat(boron waveform plating fluoride bathed) for surface mount Glossy solderPb 5.0-15.0% Ordinary glossy solder plated coat (coat for connector orthe like) Glossless solder Pb 5.0-15.0% Ordinary glossless solder platedcoat (outer solder coat)

TABLE 15 Evaluation method Evaluation items Contents Appearance Free ofspot, stain and discoloration Heat resistance heat resistance at 150° C.× 3 Hr, no expansion, peeling, discoloration and fall-off Solderability230° C. × 3 sec × once after heat resistance. Solder should be 95% ormore after soaking Bending 180° C. after heat resistance. No platingseparation in bend-back test Melt test No coat offset whennon-heat-resisted product is heated at 270° C. × 30 min and cooled andcondensed Peeling Cut a sample after heat resistance with a cutter,apply a cellophane tape and remove it, and plating should not be peeled

TABLE 16 Evaluation method Evaluation items Contents Melting Measuredtemperature at end of point (° C.) melting using METTLER FP900 thermosystem Solder Measured five times under the wettability followingconditions using zero-cross time, wet strength measuring conditions,solder checker (SAT-2000) Sn 605, Pb 40%, TEMP 230° C., PEED 25 mm/sec,DEPTH 2 mm flux present “zero-cross (sec) wet strength (mg)” samplesbefore and after heat resistance n = 5 Vickers hardness Measurednon-heat-resisted samples under the following conditions by using asuper light load minute hardness meter (model mvk-1). load: 0.5 gf, loadkeeping time: 15 sec, load speed: 0.01 mm. Measured the diagonal line ofa dent three times and computed the Vickers hardness from the averagedent area Bonding strength Sampled ten samples at a width of 3 mm. (kg)Place cut samples one on another with a clearance of 0.3 mm andsolder-dip them under the following conditions using a solder checker.sn 60%, Pb 40%, EMP 230° C., SPEED 25 mm/sec. DEPTH 2 mm. Flux present.Measured force to separation using a push-pull gauge. Samples before andafter heat resistance n = 3 Plating thickness Measured with afluorescent X-ray (μm) film thickness measuring unit Composition (%)Pb-less plating . . . Measured by SEM Pb-less So (Scannig ElectronMicroscope). N = 3 So plating . . . Measured with a fluorescent X-rayfilm thickness measuring unit. N = 5

EXAMPLES

Examples of this invention will now be described with reference to theaccompanying drawings. In the diagrams, “1” is a lead frame where amount component, such as an IC chip, is mounted, and which has an islandportion 2 in the center portion and a plurality of outer leads at theperiphery.

“3” denotes outer leads which become to-be-plated portions and protrudeoutward of the IC package, and “4” is a ball lead portion which becomesa to-be-plated portion as external leads of CSP.

While alloy plating to be applied to the aforementioned to-be-platedportions contains Sn and a plating material other than lead, and thecomposition is as follows. The set ratios are Bi=1.0% with respect toSn=99.0% in the first example, and Bi=2.0 to 10.0% with respect toSn=98.0 to 90.0% in the second example. The ratio is set to Ag=1.0 to3.0% with respect to Sn=99.0 to 97.0% in the third example. The ratio isset to Ag=3.0 to 5.0% with respect to Sn=97.0 to 95.0% in the fourthexample. The ratio is set to Ag=8.0 to 10.0% with respect to Sn=92.0 to90.0% in the fifth example. The ratio is set to Cu=0.5 to 1.0% withrespect to Sn=99.5 to 90.0% in the sixth example.

“5” is an IC chip, a mount component, to be mounted on the lead frame 1,“5′” is an LSI chip, and “5″” is a chip tantalum capacitor. “6” denotesinner leads, and “7” is a package which has the IC chip 5 or the LSIchip 5′ molded with a resin. FIG. 8 shows an IC wafer.

In FIG. 6, “8” is an IC wafer in a pretreatment in the IC fabricationprocess, and a plurality of patterns are formed on the IC wafer of 150to 200 mm in diameter.

[Specific Examples of Steps]

(1) IC Fabrication Process

-   -   a. IC wafer step=form a plurality of patterns on the IC wafer        (FIG. 6) of 150 to 200 mm in diameter. There are actually over        300 steps to this step.    -   b. Dicing=dice the IC wafer 8 into individual semiconductor IC        chips 5 (FIG. 6). The above are pretreatments.    -   c. Die bonding=adhere and fix the IC chip 5 to the island        portion 1′ of the lead frame 1 (FIG. 7).    -   d. Wire bonding=bond the IC chip 5 to electrodes 3′ of the lead        frame 1 and the inner leads 6 (FIG. 7).    -   e. Resin mold=perform resin molding to form and protect the        package 7 (FIG. 8). The above are post-treatments.        (2) IC Assembling Step    -   a. IC lead frame forming=form the elongated lead frame 1 by        press punching and photoetching a rolled thin metal plate (42        alloy, copper alloy) (chain-line portion in FIG. 6).    -   b. Inner plating=apply gold plating or silver plating to the IC        lead frame (island portion 2 and inner leads 6) before resin        molding (FIG. 6).    -   c. Die bonding and wire bonding bond the IC chip 5 to the island        portion 2 of the lead frame. Then, connect the IC chip 5 to the        electrodes 3′ of the lead frame 1 by the inner leads 6 (FIG. 7).    -   d. Resin molding=Seal and fix the IC chip 5 and the inner leads        6 in the package 7 with plastic, such as epoxy resin or silicon        resin (FIG. 8).    -   e. Baking=perform a high-temperature treatment for stabilization        after resin molding.    -   f. Resin variable removal=remove a thin resin coat sticking out        over the lead frame 1 at the time of resin molding. Thereafter,        perform honing with water jet, resin or glass beads.    -   g. Outer plating=Plate the outer leads 3 with a Pb-free material        according to this invention containing Sn as an essential        component and Bi, Ag or Cu by using an electrolytic process with        a special waveform with a melting point in a range of 220 to        250° C. That is, as the aforementioned alloy plating material,        Bi is set to or less 1.0% with respect to Sn=99.0% in the first        example, Bi is set to 2.0 to 10.0% with respect to Sn=98.0 to        90.0% in the second example, Ag is set to 1.0 to 3.0% with        respect to Sn=99.0 to 97.0% in the third example, Ag is set to        3.0 to 5.0% with respect to Sn=97.0 to 95.0% in the fourth        example, Ag is set to 8.0 to 10.0% with respect to Sn=92.0 to        90.0% in the fifth example, and Cu is set to 0.5 to 1.0% with        respect to Sn=99.5 to 90.0% in the sixth example.    -   h. Cutting=cut away the individual IC packages 7 from the linked        frames (chain lines K in FIG. 8, chain lines K in FIG. 5).    -   i. Bend the outer leads 3 according to the intended mounting        (FIG. 2 shows mounting on a printed circuit board).    -   j. Mount the IC package 7 on an electrode pattern 10 of a        printed circuit board 9 and solder bonding portions to the outer        leads 3 (FIGS. 2 and 3). In this case, it is placed on the        electrode pattern 10 of the printed circuit board 9 that faces        the ball leads 4 of BGA or CSP (FIG. 4).

[Effect of the Invention]

With the above-described structure, this invention eliminates Pb from asolder material as a bonding material which is essential for electroniccomponents in the production of electronic devices, thereby preventing apossible pollution problem such that when electronic devices whichbecome unnecessary are disposed of, Pb leaks and seeps into groundwater.

In mounting electronic components, alloy plating equivalent to orgreater than Pb can be acquired without using Pb but by using otherbonding materials than Pb.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of one piece of a frame 1.

FIG. 2 is a perspective view of an IC package that packages an IC chipto which alloy plating is applied with a substitute bonding material forPb according to this invention is mounted on a lead frame.

FIG. 3 is a cross-sectional view of an IC package to which alloy platingis applied with a substitute bonding material for Pb according to thisinvention and which is mounted on a printed circuit board.

FIG. 4 is a cross-sectional view of an LSI package to which alloyplating is applied with a substitute bonding material for Pb accordingto this invention and which is mounted on a printed circuit board.

FIG. 5 is a plan view of a chip tantalum capacitor mounted on a leadframe.

FIG. 6 is a perspective view of dicing and die bonding in the ICfabrication process.

FIG. 7 is a perspective view of wire bonding in the IC fabricationprocess.

FIG. 8 is a perspective view of packaging a lead frame with resinmolding.

DESCRIPTION OF REFERENCE NUMERALS

A first measuring portion

B second measuring portion

a third measuring portion

b fourth measuring portion

1 lead frame

2 island portion

3 outer leads

4 ball lead portion

5 IC chip

6 inner leads

7 IC package

8 IC wafer

9 printed circuit board

10 electrode pattern

11 soldering bonding portion

1. A process for functional alloy plating using substitute bondingmaterial for Pb, comprising applying functional alloy plating to anelectronic component to be mounted using an electrolytic process with apulse waveform, said functional alloy plating comprising Sn as base, andCu, wherein said Cu content to said Sn is set to 0.5 to 1.0%.
 2. Theprocess according to claim 1 wherein the pulse waveform cycles betweenpositive and negative.
 3. The process according to claim 2 wherein thepulse waveform cycling between positive and negative comprises a 6-phasehalf-wave.
 4. The process according to claim 3 wherein the 6-phase halfwave comprises a thyristor 6-phase half wave.
 5. A process forfunctional alloy plating using substitute bonding material for Pb, saidprocess comprising wire-bonding an IC chip to a lead frame, andsubjecting outer leads exposed outside a molded IC package to anelectrolytic process with an Sn content which is 99.5 to 99.0%, and a Cucontent to said Sn being set to 0.5 to 1.0% and with a pulse waveform.6. The process according to claim 5 wherein the pulse waveform cyclesbetween positive and negative.
 7. The process according to claim 6wherein the pulse waveform cycling between positive and negativecomprises a 6-phase half-wave.
 8. The process according to claim 7wherein the 6-phase half wave comprises a thyristor 6-phase half wave.9. A process for functional alloy plating using substitute bondingmaterial for Pb comprising subjecting an electrode pattern of a printedcircuit board to an electrolytic process with an Sn content which is99.5 to 99.0%, and a Cu content to said Sn being set to 0.5 to 1.0% andwith a pulse waveform.
 10. The process according to claim 9 wherein thepulse waveform cycles between positive and negative.
 11. The processaccording to claim 10 wherein the pulse waveform cycling betweenpositive and negative comprises a 6-phase half-wave.
 12. The processaccording to claim 11 wherein the 6-phase half wave comprises athyristor 6-phase half wave.
 13. A process for functional alloy platingusing substitute bonding material for Pb comprising wire-bonding a chiptantalum capacitor to a lead frame, and subjecting outer leads exposedoutside said chip tantalum capacitor to an electrolytic process with anSn content which is 99.5 to 99.0%, and a Cu content to said Sn being setto 0.5 to 1.0% and with a pulse waveform.
 14. The process according toclaim 13 wherein the pulse waveform cycles between positive andnegative.
 15. The process according to claim 14 wherein the pulsewaveform cycling between positive and negative comprises a 6-phasehalf-wave.
 16. The process according to claim 15 wherein the 6-phasehalf wave comprises a thyristor 6-phase half wave.
 17. A process forfunctional alloy plating using substitute bonding material for Pbcomprising subjecting general electronic device component materialsincluding a component material which needs plating for bonding and ageneral component material which needs plating as a functional componentto an electrolytic process with an Sn content which is 99.5 to 99.0%,and a Cu content to said Sn being set to 0.5 to 1.0% and with a pulsewaveform.
 18. The process according to claim 17 wherein the pulsewaveform cycles between positive and negative.
 19. The process accordingto claim 18 wherein the pulse waveform cycling between positive andnegative comprises a 6-phase half-wave.
 20. The process according toclaim 19 wherein the 6-phase half wave comprises a thyristor 6-phasehalf wave.